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I'm not sure if a Mac 7440 is legal on a C90 at the full 74 inches but I have heard that they work well From what I can gather, the general consensus is to use the Sensenich 76-AK-2 series for a long prop on the C90. It's a 76" whittled down to 74". Some of us impatient ones just don't want to wait for one from the factory.

I know nothing of performance on floats. On wheels, I do know that if you trade a 7148 cruise for a little longer one with a 40 pitch it's not even the same airplane! If I recall correctly, a good number of the float guys are using a 38 pitch.

Looks like you're getting good rpm already. Not sure if the extra diameter will make a noticeable difference.

I'm not sure if a Mac 7440 is legal on a C90 at the full 74 inches but I have heard that they work well From what I can gather, the general consensus is to use the Sensenich 76-AK-2 series for a long prop on the C90. It's a 76" whittled down to 74". Some of us impatient ones just don't want to wait for one from the factory.

I know nothing of performance on floats. On wheels, I do know that if you trade a 7148 cruise for a little longer one with a 40 pitch it's not even the same airplane! If I recall correctly, a good number of the float guys are using a 38 pitch.

Looks like you're getting good rpm already. Not sure if the extra diameter will make a noticeable difference.

7440

Had 7440 on j3 with C85 don't see why you could not put on C90
I do believe the longer the better for sea plane especially in hot weather.
I am sure some of the guys on his site can answer you better on legal questions.

I didn't have time to try rpm at 50 mph climb, or indicated stall speed at WOT. Got dark on me.
Some observers were stepping off takeoff roll as 130 to 150 feet, but I don't believe them.
Deck angle at low speed climb WOT was impressive.
Acceleration after liftoff to climb speed was impressive
Acceleration during ground roll was improved.
Prop was quite smooth.
I was impressed

No, I'm not saying that I would prefer to run the 7535. There are five classes of overspeed (Categories Ia, Ib, IIa, IIb, and III). Running an O-200, you can easily reach a IIb overspeed with the 7545 (I was careful not to exceed IIa, which has the same inspection requirements as Ib). You can probably reach IIb with a C90 as well. A IIb overspeed would require that you replace the rod bolts and nuts, among a number of other unpleasant and potentially more expensive consequences. I've run a 7441, liked it, think a 7440 would do better than the 41, and that a 39 might be better still (I'm not in a hurry to get anywhere in a cub). Any flatter, and you run a severe risk of hurting the engine. I run a 7142 on a daily basis and think that on an O-200 (and probably a 90) it is a great compromise prop that won't lead a prudent pilot to hurt the engine. Being careless with the 7545 could lead to the need for an overhaul or worse within a very short period of time. That said, the 7545 performance is quite impressive, including a 55 mph climb at full rated rpm (2750 rpm) on a 95 degree day -- the 7545 just comes with a potentially exorbitant penalty.
JimC

>ie. ... would a 7440 with 2450 static outperform a 7140 with 2550 static?<

The nearest I can come to responding to this question is to say that a 7142 slightly outperforms a 7441 in every aspect, static rpm, climb rpm, and cruise speed. I would expect a 7142 to match a 7440 in static and climb, and to outrun the 7440 in cruise. A 7140 would climb even better, but would probably cruise 3 or 4 mph slower.

I've run wood and aluminum props of identical diameter and pitch (7443) back to back within 30 minutes of one another. Typically, the takeoff roll is about 10-15% longer with the wood prop, and the wood prop cruises 8 to 10 mph slower. It doesn't climb as well either.

I've also run a 7438 on an 85 powered J3 and agree about the great climb and terrible cruise.
JimC

Hi,
In another thread I am in a similar boat or plane as it is. I have a Mc Cm 7443 on my J3C-65 now. Just completd majoring a C90-8 for the cub. For that engine on a cub McCauley calls for a 7148. It seems everyone is talking about 40-42" pitch on these props. A-691 spec for the J3 says for a J3 with a C-90-8F engine limits are 2475rpm at takeoff. So wouldn't a 40-42" pitch overspeed the engine? I am kinda new to all this prop stuff and maybe I am mising something here. The 0200 on the other hand does require a higher rpm to get the HP and I thought this was one of the reasons a C90 was a better option on a Cub.

Oh just thought of another thing. Yes, the 74" version of the Mc CM props are not legal on a C90. Some time ago I talked with Cris Bell an engineer at McCauley and he told me the limit on a C90 was 73" due to some harmonic problems in the longer lengths. The problem is that they never certified it on a J3 with a C90.

Tom
I run a 71/48 for longer trips. It is a faster cruise but a real dog for all other operations. I Just had my 71/44 repitched to a 71/40 for seaplane operations and it works great. I really liked the 71/44 for a general/ all purpose prop. Now I need to find another one of those. This is on a C-90-8F

>A-691 spec for the J3 says for a J3 with a C-90-8F engine limits are 2475rpm at takeoff. So wouldn't a 40-42" pitch overspeed the engine?<

Not if you don't shove the throttle all the way forward. Just put a stick-on label on the panel that says, "Never Exceed 2475 RPM" and a red line on the tach at the same rpm. I know of two J3's that are legally running O-200's and 7142's approved by 337 that spell out use of that method to limit rpm to 2640 and horsepower to 85. I doubt that your 90 will turn the 7142 quite as fast as the O-200 does anyway. If it does, repitch the prop steeper to slow it down. Costs about $150. Run it first at its present pitch and before repitching it, record the pertinent rpms, and use those as a guide to decide what final pitch you want. Right now, with the 95 degree weather, my brother's O-200 is staticing the 7142 at 2550 t0 2575 rpm, and is turning about 2640 during a 60 mph climb with one on board the J3 and about 2600 with two. With the 7142, in 95 degree weather, you'll cruise at about 78 to 80 mph at 2350 rpm.

Be sure to read SB05-2 on what actions are required after the 5 different classses of engine overspeeds. They range from no action required for Category IA to a minimum of complete overhaul and replacement of specified parts for a Category III excessive overspeed.

Note that although A-691 limits maximum power for ALL operations to 90 hp at 2475 rpm, the C90 Type Certificate (E252) allows it to turn 2625 rpm for 5 minutes, producing 95 horsepower for climbout. You can't reach that rpm with more than a 42 pitch. However, A-691 also limits maximum static to 2350 rpm, which requires roughly about a 44 to 45 inch pitch. This is why an O-200 J3 will blow the socks off a C90 J3 in climb unless the 90 is running the flatter prop and going by E252 instead of A-691 (which isn't really allowed, but some C90 pilots ignore it).
JimC

I'm also thinking about a new prop for my experimental cub. It looks like a J3, but is really more like a PA-11 with its wing tanks. My O-200 was converted to a -8 by Don Swords of Don's Dream Machines.

My current prop is a wood Sensenich W72GK44. It gets 2275 rpm static, 2375 rpm at 60 mph climb, and 2550 - 2575 rpm at full throttle at about 95 mph. This is at about 600' msl and 90 degrees F.

My take-off and climb performance is pretty good now, but I'm thinking that a more efficient metal prop with a finer pitch it could improve quite a bit.

From posts on this thread, it sounds like a McCauley 1B90 CM7142 would be a good choice. By the way, is the squared tip of the 1B90 more efficient than the elliptical tip 1A90?

>From posts on this thread, it sounds like a McCauley 1B90 CM7142 would be a good choice. By the way, is the squared tip of the 1B90 more efficient than the elliptical tip 1A90?<

The 7142 would be an excellent choice for an O-200 PA-11 clone, though with the lower drag of the -11 vs. the -3, you might consider a 7143 instead. You'd sacrifice a bit of ground roll with the 43, but the lower drag -11 with a 7143 would probably still outclimb a -3 with a 7142 (I'm thinking about going the other direction, repitching the 7142 on an O-200 J3 to 7141).

For a given airfoil distribution, an elliptical tip is slightly more efficient than a squared tip, but that difference is negligible between a 1A90 and a 1B90 and probably swamped by the other differences in those two propellers. If I were going for an extreme cruise prop, given the same airfoil distribution on two props, I'd probably prefer an elliptical tip. If I were going for a climb prop, I'd probably prefer the square tip. But, as a practical matter, on a J3 or PA11 the difference in tip shape isn't really worth worrying about.

To get a feel for the performance gross weight performance of the 7142 on an O-200 J3, last Saturday, the OAT was about 95 degrees at 310 MSL. We did a reduced power cruise climb (60 mph at 2500 rpm -- full throttle holding that airspeed would have been about 2640 rpm) from 310 MSL to 6000 PA with weight at and near gross. At 6000 feet PA, we were still climbing at about 600 fpm with throttle retarded to 2500 rpm. Oil temperature reached about 180 degrees indicated, compared to the usual 140 degrees (uncalibrated J3 temperature gauge -- don't know what the real oil temperature was). On an O-200 PA-11, you'd climb a lot better than that, but the oil temps would be substantially higher.

With a given pilot/passenger load, it depends upon the amount of fuel you're carrying. If you can carry more than 12 gallons, you'll have more induced drag than the J3 when you are carrying more than 12 gallons. Once your fuel burns down to 12 gallons or less, induced drag will be equivilent. The J3 that I fly doesn't have the wingtanks. We preferred to stay with the stock nosetank and have a removable external 10 gallon belly tank that can be installed for long trips.
JimC

J3/PA11 Exp Prop

Clyde,
Legend uses a Sensenich 72 X 46 wood core composite covered prop with their O-200 powered open cowl Legend Cub. This prop is light and smooth like your wood prop, but has almost the same performance and durability as the metal prop. Contact Sensenich Wood Propeller for more info.

The Sensenich composite prop sounds like a really interesting compromise between the wood and metal props. Do you know if they are usable on certified airplanes (Cubs) or are they only usable on LSA's?

John Scott

While I respect the folks that use Cubs to make a living, my uses are for recreation and leisure - AND I'M NOT ASHAMED!!!

I can take some. They belong to two of my friends. Their dad designed and built two, installing them on his two J3's by 337. The two sons each inherited one of the J3's. The tanks are really neat and take less than an hour to install or remove.
JimC

Generally an old rule of thumb is that if you increase the diameter 1" you reduce the pitch 1". The result should give you slightly better acceleration and climb performance due to the larger diameter of the prop blast. The engine likely will seem smoother due to the better flywheel action. A long slow turning prop will give more thrust thus better performance on slower Cub type airplanes. On higher speed planes the long prop will generate more drag. Generally the prop diameter is restricted by ground clearance requirements, which is why a float plane is able to use a longer prop. Years ago I experimented with several different props on a 150 hp 7GCB on floats. The original prop was a 7456. The cruise was about 103 mph. I settled on a 8046 prop. I know this doesn't follow the rule of thumb. The cruise remained the same while the take off time was reduced by 1/3 and the rate of climb was increased by about 1/3. It also ran a lot smoother. I also ran this prop on wheels (8.50 x6) with excellent performance.

McCaully 7140 vs 7440

Hi guys I have a pa-11 with a c90-8 have a 7144 and a 7440 the 7144 seemed to get off better on wheels and floats but the 7440 was better on skis, did some upgrades and now run the 7440 all the time and turn about 2475 on t/o but have to throttle to about 1/2 throttle in level flight, may not be quite legal but it's a lot more fun. also have the 25x11x4 Goodyear tire so prop clearance is no problem.